Micromirrors may be used in various optical applications instead of, or in addition to, conventional optoelectronic devices. It is desirable to have capability to move the micromirrors by rotation and translation with very fine control.
Since the micro-electro mechanical systems (MEMS) were developed, many applications in MEMS have been developed and used. Micromirror device is the one of the major development in MEMS field. Devices and application using micromirrors are developed and used in various fields such as optical communication and display. As the applications of micromirrors grow rapidly, the demand on controlling micromirror device increases. It is desirable to have the motion control of the micromirror with many degrees of freedom and simple driving method.
A phase-only piston-style micromirror has been used for phase adaptive optics applications and a rotational micromirror has been used to deflect light. Most of these micromirrors have been controlled to have continuous displacements, which are determined at the equilibrium between electrostatic force and elastic force.
U.S. Pat. No. 6,906,848 to Aubuchon discloses a micromirror device capable of tilt and phase correction using multiple electrodes. This system, however, is operated in the analog mode to provide continuous displacement. The analog control requires a fine voltage control and is more complex than the digital or discrete control and difficult to combine with known semiconductor electronics technologies such as MOS, CMOS, etc. In addition, the micromirrors with continuous displacement actuated by electrostatic force undergo the classical snap-down phenomenon when the electric force exceeds the elastic force of mechanical structure. The snap-down phenomenon limits the translational and rotational ranges of a micromirror. Furthermore, considering the number of micromirrors in the micromirror array which can be reached to tens of millions and the number of electrodes required for each micromirror, digitally or discretely controlled micromirror array systems can be more advantageously used. Even in the case using digital addressing for this system, it still has the limitation in the translational and rotational ranges of the micromirror in order to provide multiple motions of the micromirror while avoiding the snap-down phenomenon.
The high driving voltage is another disadvantage in controlling the micromirror motion with continuous displacement actuated by electrostatic force. To be compatible with IC components, it is desired that micromirrors are operated at a low voltage which is compatible with the circuit operation or control voltage.
In a prior art micromirror array, such as, for example, the digital micromirror device (DMD) in U.S. Pat. Nos. 4,566,939, 5,083,857, and 6,232,936, each micromirror is actuated by digital control of a voltage. It has large rotation, low driving voltage, and is compatible with known semiconductor electronics technologies. However, it has only one degree of freedom, that is, rotation about a single axis, and it only has two level positions.
Therefore, the demand on the simple control of the micromirror with higher degrees of freedom has been increased for using the micromirror. The present invention is intended to provide a micromirror device with multiple motions, variable degrees of freedom, low driving voltage, and simple activation mechanism. This control system can have one degree of freedom rotational motion, one degree of freedom translational motion, one degree of freedom rotational and one degree of freedom translational motion, two degrees of freedom rotational motion, and two degrees of freedom rotational motion and one degree of freedom translational motion, depending on its system configuration.